Stud or bolt

[Frank II]

Trying to remove rounded copper locknuts from ex. man. I would rather replace w/ bolt instead of stud. So I am looking for real advise from someone in the know.

 

[jranmann]

I would use me, as I am a stud (or so I hear?)
:mrgreen:

BMW does not use copper unless they feel there's a reason...and there is.
And to prove it I will suggest as above:

The copper nuts are used on the manifold to prevent just this occurance.
They are to be replaced every time you R/R same.
(the copper keeps a regular headed nut from heat damage destruction)
Also so one does not 'turn the stud out' when you are just R/R the manifold.

So someone did not replace them the last time the manifold was removed...
If that was you...shame and you deserve this upcoming lesson in M30 machining!

(keep it studs and copper nuts) and next time, pay attention!

but don't feel bad as all of us have done this, at one time or another...


lol!

Ran

 

[Bertocchi]

When you go to put the manifold back on you will know why studs are preferred. The studs will automatically locate both the gasket and the manifold. It is very difficult to do with bolts. The gasket shifts. does not line up, etc...
Ran gives good advice about the copper nuts. Technically the same holds true with nylon locking nuts, use them once and then replace.

 

[jranmann]

Ran gives good advice about the copper nuts. Technically the same holds true with nylon locking nuts, use them once and then replace.

See, told you I was a stud!

BMW uses copper as the parts heat and expand at different rates with the exhaust heat, if not, the materials (anything common on the periodic table) will fuse together making any nut strip or unwind the stud.

That's what's great about the old BMW engineers they thought of practically everything and when they didn't know but suspected they asked someone. This of course was back in the day before they engineered the airplane engines and just carried through..

Cheers from the machine shop!

Ran

 

[nashvillecat]

When you go to put the manifold back on you will know why studs are preferred. The studs will automatically locate both the gasket and the manifold. It is very difficult to do with bolts. The gasket shifts. does not line up, etc...
Ran gives good advice about the copper nuts. Technically the same holds true with nylon locking nuts, use them once and then replace.

I agree with the wisdom of using CU based nuts with steel studs and the fact that assembly is easier with studs. (Same reason some prefer lug nuts to lug bolts when installing wheels). In addition to any favorable chemistry presented by the copper alloy/steel combination, the copper nuts are designed with a gap that crushes against the threads, making it "self locking," or at least not requiring a lock washer. Nevertheless, other manufacturers and respected engine builders have successfully used all sorts of steel-on-steel fasteners to secure exhaust parts. An appropriately placed dab of antiseize paste, a lock washer, or even stainless fittings can be worthy alternatives.

I haven't given this issue much thought, but I far from certain BMW always used the copper alloy nuts for exhaust manifold. And - if given the right circumstances, removal of a soft rounded copper nut can still be annoying if not unpleasant.

More to the point of the original post, I have seen the use of bolts, in limited circumstances, to speed the process of manifold removal, especially when using custom parts (big headers) or where there are other interference issues. If one leaves a steel nut to bond itself to the stud, it becomes a defacto bolt and theoretically reusable as such. Not a recommended procedure for the reasons stated. If you were using "square stove bolts" on old cast iron machinery pre-modified with bailing wire, I won't tell - but the exhaust leak may be a giveaway and even scare off unwanted varmints. :lol:

Other lesser considerations for using studs versus bolts is the fact that the cylinder head threads are aluminum and probably not the best material for repeated over-torquing with small threads. The softer metal generally loses in a tug-o-war with stronger metal. (Yes, I am aware that spark plugs are repeatedly torqued using the same materials and I am not saying it won't work). Secondarily, you risk an oil leak where the stud seals an oil passage.

hth :?:

 

[Frank II]

OK, I get it. Thanks for all posts. It would appear the previous wanted to replace the gaskets, rounded off three locknuts and reassembled. I was thinking of headers, but have euro engine w/ good manifold which I will clean up and powdercoat. Thanks again! looks like dremel cutoff wheels will be busy